A plastic container is easy to form, can be inexpensively produced and has, therefore, been widely used in a variety of applications. For instance, a container of which the inner wall surface is formed by using an olefin resin such as polyethylene, has been used as a container for containing viscous slurry-like or paste-like contents.
The plastic container containing a viscous content is, in many cases, preserved in an inverted state so that the viscous content filled therein can be quickly discharged or can be used up to the last drip without being left in the container. It is, therefore, desired that when the container is inverted, the content which, for example, may be viscous quickly falls down without staying on the inner wall surface of the container.
As for packing containers for containing viscous non-oily materials as represented by ketchup, in recent years, a variety of proposals have been made in regard to letting nearly the whole amount of the viscous content be quickly discharged out of the container without adhering on the container wall surfaces.
For example, a patent document 1 is proposing a polyethylene container used for containing the ketchup, wherein a polyethylene layer forming the inner surface is blended with an aliphatic amide and, specifically, with an unsaturated aliphatic amide such as oleic acid amide or ethylenebis oleic acid amide as a lubricating agent, or is blended with an organic peroxide together with these aliphatic amides.
The patent document 1 is a patent application filed by the present applicant and teaches that the container disclosed therein enables the non-oily viscous content such as ketchup to fall down excellently when it is inverted. When the contents are hot-filled, addition of the aliphatic amide only is not enough for letting the contents fall down by inverting the container. According to the patent document 1, therefore, the organic peroxide is also added in combination therewith to maintain a high level of content fall-down performance by inverting the container even in case the contents are hot-filled.
Patent documents 2 and 3, too, are the patent applications filed by the present applicant. The patent document 2 describes that upon forming a polymolecular structure of aliphatic amide (amphipatic molecules) and, specifically, saturated aliphatic amide stemming from the lubricating agent in the resin layer on the inner surface of the container, the non-oily viscous content such as ketchup can be excellently fallen down by inverting the container despite the non-oily viscous content was hot-filled.
The patent document 3 proposes the use of a saturated aliphatic amide having not less than 18 carbon atoms and, specifically, the use of a behenic acid amide as a lubricating component in the olefin resin layer on the inner surface of the container, and describes that this produces excellent inverted fall-down performance even in case the non-oily content is hot-filled.